The Continental Deka VII fluid injector has traditionally been used only for low pressure multipoint gasoline engine fuel delivery systems. The absence of oxygenates in gasoline reduced the potential for corrosive attack on the injector fluid path components. In recent years, the Deka VII injector has been modified for use in exhaust after-treatment systems where the working fluid can be aqueous urea solution (AUS-32), with a heightened potential for corrosion. Alternatively, the fuels used for gasoline engines now have an increasing content of ethanol (an oxygenated fuel), and in some markets such as Brazil, the fuel can be often predominantly composed of ethanol. There are also modified configurations of the injector for the high ethanol content applications that provide active heating of the fuel, further increasing the potential for corrosive attack. The current configuration of the Deka VII (and next generation Deka) injector includes a weld of two subcomponents that are in a location where corrosion processes could be facilitated, leading to possible damage and failure of the injector when used in these corrosive environments.
With reference to FIGS. 1-3, the conventional Continental Deka VII fluid injector, generally indicated at 10, is a low pressure solenoid fluid injector which uses a standard ball 12 associated with on a conical valve seat 14, and orifice plate spray generator or metering disk 16 which is in widespread use for port gasoline injection. When the injector coil 18 is energized, the armature 20 is drawn to the stator 22, or pole piece. The armature 20 is connected to the metering ball 12 by a tube 24. Thus, the ball 12 is lifted off the injector valve seat 14 to allow pressurized fluid to flow across a metering disk 16.
With reference to FIG. 3, the armature-tube-ball assembly consists of three components that are welded together. The fluid flows through a hole 21 drilled through the longitudinal axis of the armature 20 into the tube 24. Surfaces in the tapered area of the tube 39 define at least one through-hole 26 that is disposed transversely with respect to a longitudinal axis of the tube 24. Due to cost considerations, the configuration uses a ball bearing as ball 12 and a drawn tube 24 which are laser welded together at weld 30 (FIG. 4).
The resultant weld joint creates a crevice volume V on the “back” side of the ball 12. This crevice volume V is in a zone Z (FIG. 3) where fluid is presumed to be mostly stagnant. The corrosion resistance of the material in the weld heat affected zone also tends to be somewhat weakened, despite the fact the materials of the welded subcomponents are stainless steels. The welding process can lead to a destruction or occupation of chromium sites, which form the passive oxidation layer that provides the corrosion resistance properties of stainless steels. Testing has shown that the combination of stagnant oxygenated fluid in the crevice volume and materials with weakened resistance leads to corrosion of this joint. The absence of corrosion on the “outside” surface of the joint is a result of a smooth flat surface and continual fluid flow across this surface.
Thus, there is also a need to eliminate the exposure of the weld zone inside the injector tube to the working fluid in a cost-effective manner.